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Abstract CHIME (chemical Th-U-total Pb isochron method) ages were determined for monazite from gneisses and granitoids of the Ryoke belt in the Iwakuni area. The CHIME monazite ages are 99.6 ± 2.4, 98.9 ± 2.1 and 98.2 ± 5.7 Ma for the Ryoke gneiss, 90.7 ± 2.2, 89.7 ± 2.0 and 89.3 ± 2.2 Ma for the Tajiri Granite, 91.0 ± 3.2, 90.6 ± 3.2 and 89.9 ± 3.2 Ma for the Namera Granite, 89.3 ±3.3 and 88.6 ± 5.6 Ma for a small stock at Shimizu, and 87.3 ± 1.6 and 86.6 ± 2.1 Ma for the post-tectonic Shimokuhara Granite. The CHIME monazite ages, interpreted as the time of the first attainment at the amphibolite facies conditions for the gneisses and as the time of emplacement for the granites, respectively, agree with the field intrusive sequence. The present dating documented that the Ryoke metamorphism in the Iwakuni area reached the amphibolite facies conditions at ∼98 Ma, was complete at -87 Ma, the time of emplacement of the post-tectonic Shimokuhara Granite.  相似文献   
34.
A new multi-anvil type high-presure apparatus has been developed using sintered diamond anvils to generate pressures over 30 GPa and temperatures up to about 2000°C. A maximum sample volume of about 1 mm3 is available in this system. The pressure was confirmed by dissociation of forsterite into Mg-perovskite and periclase. The basic techniques and problems in utilizing sintered diamond in the MA8 type high-pressure apparatus are discussed with an emphasis on the future prospect of incorporating simultancous X-ray diffraction observation.  相似文献   
35.
Convective instability and overstability of a plane-parallel medium in the presence of a uniform vertical magnetic field is studied. We take into account both the effect of penetration of disturbances into sub-adiabatically stratified semi-infinite upper and lower layers, and the effect of thermal damping of disturbances introduced by the compressibility of the medium. If the degree of super-adiabaticity in temperature stratification in the middle layer is relatively large compared with that of sub-adiabaticity in the upper and lower layers, the range of physical conditions in which overstable convection occurs is very narrow. However, if it is not the case the range is rather wide. In the normal sunspot umbra, only disturbances with selected sizes in vertical dimension will be able to become overstable. The overstable convection might be a cause of some dynamical features (such as dots) in the sunspot umbra, but will not be the main contributor for transporting mechanical energy in the sunspot region.  相似文献   
36.
The North Anatolian fault zone that ruptured during the mainshock of theM 7.4 Kocaeli (Izmit) earthquake of 17 August 1999 has beenmonitored using S wave splitting, in order to test a hypothesisproposed by Tadokoro et al. (1999). This idea is based on the observationof the M 7.2 1995 Hyogo-ken Nanbu (Kobe) earthquake, Japan.After the Hyogo-ken Nanbu earthquake, a temporal change was detectedin the direction of faster shear wave polarization in 2–3 years after the mainshock (Tadokoro, 1999). Four seismic stations were installed within andnear the fault zone at Kizanlik where the fault offset was 1.5 m, about80 km to the east of the epicenter of the Kocaeli earthquake. Theobservation period was from August 30 to October 27, 1999. Preliminaryresult shows that the average directions of faster shear wave polarization attwo stations were roughly parallel to the fault strike. We expect that thedirection of faster shear wave polarization will change to the same directionas the regional tectonic stress reflecting fault healing process. We havealready carried out a repeated aftershock observation at the same site in2000 for monitoring the fault healing process.  相似文献   
37.
A theoretical light curve is constructed for the quiescent phase of the recurrent nova U Scorpii in order to resolve the existing distance discrepancy between the outbursts (d approximately 6 kpc) and the quiescences (d approximately 14 kpc). Our U Sco model consists of a very massive white dwarf (WD), an accretion disk (ACDK) with a flaring-up rim, and a lobe-filling, slightly evolved, main-sequence star (MS). The model properly includes an accretion luminosity of the WD, a viscous luminosity of the ACDK, and a reflection effect of the MS and the ACDK irradiated by the WD photosphere. The B light curve is well reproduced by a model of 1.37 M middle dot in circle WD + 1.5 M middle dot in circle MS (0.8-2.0 M middle dot in circle MS is acceptable) with an ACDK having a flaring-up rim and the inclination angle of the orbit i approximately 80&j0;. The calculated color is rather blue (B-V approximately 0.0) for a suggested mass accretion rate of 2.5x10-7 M middle dot in circle yr-1, thus indicating a large color excess of E(B-V) approximately 0.56 with the observational color of B-V=0.56 in quiescence. Such a large color excess corresponds to an absorption of AV approximately 1.8 and AB approximately 2.3, which reduces the distance to 6-8 kpc. This is in good agreement with the distance estimation of 4-6 kpc for the latest outburst. Such a large intrinsic absorption is very consistent with the recently detected period change of U Sco, which is indicating a mass outflow of approximately 3x10-7 M middle dot in circle yr-1 through the outer Lagrangian points in quiescence.  相似文献   
38.
We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 × 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 × 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 m dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92° × 1.38° per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration.  相似文献   
39.
Freezing was used in the jointing section of two shields (diameter 3.14 m) which ran across at right angles and at 25-m depth under the crossing of main roads for the construction of a 2.4-m diameter sewer tunnel. The object of freezing was to create a frozen barrier to prevent the inflow of water and fine sand into the area to be excavated.

Thirty-five freeze pipes (length about 7 m) were placed from one shield conically in the direction of the flank of another shield with freeze pipes attached to its inside wall. The cooling unit was placed on unoccupied land at about 60 m distant from the jointing section and the freeze pipes were connected with the cooling unit by supply and return pipelines.

The cooling unit had a cooling capacity of 79,000 kcal/h at an evaporation temperature of −27°C and a condensation temperature of +40°C. Freezing was continued for 180 days and the CaCl2 brine temperature was −25 to −30°C. These works were accomplished without the sinking of shaft and the use of injection, in complete safety with no traffic restriction on the road surface.  相似文献   

40.
The mechanism of locomotion of aquatic animals can provide us with new insight into the maneuverability and stabilization of underwater robots. This paper focuses on biomimesis in the maneuvering performance of aquatic animals to develop a new device for maneuvering underwater robots. In this paper, guidance and control in the horizontal plane of a fish robot equipped with a pair of two-motor-driven mechanical pectoral fins on both sides of the robot in water currents is presented. The fish robot demonstrates high performance in terms of maneuverability in such activities as lateral swimming. The use of fuzzy control enables the fish robot to perform rendezvous and docking with an underwater post in water currents  相似文献   
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